| 1. |
- Cheung, L., et al.
(author)
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Human mediastinal adipose tissue displays certain characteristics of brown fat
- 2013
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In: Nutrition & Diabetes. - : Springer Science and Business Media LLC. - 2044-4052. ; 3:UNSP e66
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Journal article (peer-reviewed)abstract
- BACKGROUND: The amount of intra-thoracic fat, of which mediastinal adipose tissue comprises the major depot, is related to various cardiometabolic risk factors. Autopsy and imaging studies indicate that the mediastinal depot in adult humans could contain brown adipose tissue (BAT). To gain a better understanding of this intra-thoracic fat depot, we examined possible BAT characteristics of human mediastinal in comparison with subcutaneous adipose tissue. MATERIALS AND METHODS: Adipose tissue biopsies from thoracic subcutaneous and mediastinal depots were obtained during open-heart surgery from 33 subjects (26 male, 63.7 +/- 13.8 years, body mass index 29.3 +/- 5.1 kg m(-2)). Microarray analysis was performed on 10 patients and genes of interest confirmed by quantitative PCR (qPCR) in samples from another group of 23 patients. Adipocyte size was determined and uncoupling protein 1 (UCP1) protein expression investigated with immunohistochemistry. RESULTS: The microarray data showed that a number of BAT-specific genes had significantly higher expression in the mediastinal depot than in the subcutaneous depot. Higher expression of UCP1 (24-fold, P < 0.001) and PPARGC1A (1.7-fold, P = 0.0047), and lower expression of SHOX2 (0.12-fold, P < 0.001) and HOXC8 (0.14-fold, P < 0.001) in the mediastinal depot was confirmed by qPCR. Gene set enrichment analysis identified two gene sets related to mitochondria, which were significantly more highly expressed in the mediastinal than in the subcutaneous depot (P < 0.01). No significant changes in UCP1 gene expression were observed in the subcutaneous or mediastinal depots following lowering of body temperature during surgery. UCP1 messenger RNA levels in the mediastinal depot were lower than those in murine BAT and white adipose tissue. In some mediastinal adipose tissue biopsies, a small number of multilocular adipocytes that stained positively for UCP1 were observed. Adipocytes were significantly smaller in the mediastinal than the subcutaneous depot (cross-sectional area 2400 +/- 810 versus 3260 +/- 980 mu m(2), P < 0.001). CONCLUSIONS: Human mediastinal adipose tissue displays some characteristics of BAT when compared with the subcutaneous depot at microscopic and molecular levels.
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| 2. |
- Dixen, Karen, et al.
(author)
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ERR gamma Enhances UCP1 Expression and Fatty Acid Oxidation in Brown Adipocytes
- 2013
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In: Obesity. - : Wiley. - 1930-7381 .- 1930-739X. ; 21:3, s. 516-524
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Journal article (peer-reviewed)abstract
- Objective: Estrogen-related receptors (ERRs) are important regulators of energy metabolism. Here we investigated the hypothesis that ERR gamma impacts on differentiation and function of brown adipocytes. Design and Methods: We characterize the expression of ERR gamma in adipose tissues and cell models and investigate the effects of modulating ERR? activity on UCP1 gene expression and metabolic features of brown and white adipocytes. Results: ERR gamma was preferentially expressed in brown compared to white fat depots, and ERR gamma was induced during cold-induced browning of subcutaneous white adipose tissue and brown adipogenesis. Overexpression of ERR gamma positively regulated uncoupling protein 1 (UCP1) expression levels during brown adipogenesis. This ERR gamma-induced augmentation of UCP1 expression was independent of the presence of peroxisome proliferator-activated receptor coactivator-1 (PGC-1 alpha) but was associated with increased rates of fatty acid oxidation in adrenergically stimulated cells. ERR? did not influence mitochondrial biogenesis, and its reduced expression in white adipocytes could not explain their low expression level of UCP1. Conclusions: Through its augmenting effect on expression of UCP1, ERR gamma may physiologically be involved in increasing the potential for energy expenditure in brown adipocytes, a function that is becoming of therapeutic interest.
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| 3. |
- Raizen, David M., et al.
(author)
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Beyond the symptom : the biology of fatigue
- 2023
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In: Sleep. - : Oxford University Press. - 0161-8105 .- 1550-9109. ; 46:9
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Journal article (peer-reviewed)abstract
- A workshop titled “Beyond the Symptom: The Biology of Fatigue” was held virtually September 27–28, 2021. It was jointly organized by the Sleep Research Society and the Neurobiology of Fatigue Working Group of the NIH Blueprint Neuroscience Research Program. For access to the presentations and video recordings, see: https://neuroscienceblueprint.nih.gov/about/event/beyond-symptom-biology-fatigue.The goals of this workshop were to bring together clinicians and scientists who use a variety of research approaches to understand fatigue in multiple conditions and to identify key gaps in our understanding of the biology of fatigue. This workshop summary distills key issues discussed in this workshop and provides a list of promising directions for future research on this topic. We do not attempt to provide a comprehensive review of the state of our understanding of fatigue, nor to provide a comprehensive reprise of the many excellent presentations. Rather, our goal is to highlight key advances and to focus on questions and future approaches to answering them.
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| 4. |
- Abreu-Vieira, Gustavo, 1987-, et al.
(author)
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Adrenergically-stimulated blood flow in brown adipose tissue is not dependent on thermogenesis : Regulation of brown adipose tissue blood flow
- 2015
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In: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 308:9, s. E822-E829
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Journal article (peer-reviewed)abstract
- Brown adipose tissue (BAT) thermogenesis relies on blood flow to be supplied with nutrients and oxygen, and for the distribution of the generated heat to the rest of the body. It is therefore fundamental to understand the mechanisms by which blood flow is regulated and its relation to thermogenesis. Here we present high-resolution laser-Doppler imaging (HR-LDR) as a novel method for noninvasive, in vivo measurement of BAT blood flow in mice. Using HR-LDR, we found that norepinephrine stimulation increases BAT blood flow in a dose-dependent manner, and that this response is profoundly modulated by environmental temperature acclimation. Surprisingly, we found that mice lacking uncoupling protein 1 (UCP1) have fully preserved BAT blood flow response to norepinephrine, despite failing to perform thermogenesis. BAT blood flow was not directly correlated to systemic glycaemia, but glucose injections could transiently increase tissue perfusion. Inguinal white adipose tissue, also known as a brite/beige adipose tissue, was also sensitive to cold acclimation and similarly increased blood flow in response to norepinephrine. In conclusion, using a novel non-invasive method to detect BAT perfusion, we demonstrate that adrenergically-stimulated BAT blood flow is qualitatively and quantitatively fully independent of thermogenesis, and is therefore not a reliable parameter for the estimation of BAT activation and heat generation.
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| 5. |
- Fischer, Alexander W., et al.
(author)
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UCP1 inhibition in Cidea-overexpressing mice is physiologically counteracted by brown adipose tissue hyperrecruitment
- 2017
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In: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 312:1, s. e72-E87
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Journal article (peer-reviewed)abstract
- Cidea is a gene highly expressed in thermogenesis- competent (UCP1-containing) adipose cells, both brown and brite/beige. Here, we initially demonstrate a remarkable adipose-depot specific regulation of Cidea expression. In classical brown fat, Cidea mRNA is expressed continuously and invariably, irrespective of tissue recruitment. However, Cidea protein levels are regulated posttranscriptionally, being conspicuously induced in the thermogenically recruited state. In contrast, in brite fat, Cidea protein levels are regulated at the transcriptional level, and Cidea mRNA and protein levels are proportional to tissue briteness. Although routinely followed as a thermogenic molecular marker, Cidea function is not clarified. Here, we employed a gain-of-function approach to examine a possible role of Cidea in the regulation of thermogenesis. We utilized transgenic aP2-hCidea mice that overexpress human Cidea in all adipose tissues. We demonstrate that UCP1 activity is markedly suppressed in brown-fat mitochondria isolated from aP2-hCidea mice. However, mitochondrial UCP1 protein levels were identical in wildtype and transgenic mice. This implies a regulatory effect of Cidea on UCP1 activity, but as we demonstrate that Cidea itself is not localized to mitochondria, we propose an indirect inhibitory effect. The Cidea-induced inhibition of UCP1 activity (observed in isolated mitochondria) is physiologically relevant since the mice, through an appropriate homeostatic compensatory mechanism, increased the total amount of UCP1 in the tissue to exactly match the diminished thermogenic capacity of the UCP1 protein and retain unaltered nonshivering thermogenic capacity. Thus, we verified Cidea as being a marker of thermogenesis-competent adipose tissues, but we conclude that Cidea, unexpectedly, functions molecularly as an indirect inhibitor of thermogenesis.
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| 6. |
- Hagberg, C. E., et al.
(author)
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Flow Cytometry of Mouse and Human Adipocytes for the Analysis of Browning and Cellular Heterogeneity
- 2018
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In: Cell Reports. - : Elsevier BV. - 2211-1247. ; 24:10
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Journal article (peer-reviewed)abstract
- Adipocytes, once considered simple lipid-storing cells, are rapidly emerging as complex cells with many biologically diverse functions. A powerful high-throughput method for analyzing single cells is flow cytometry. Several groups have attempted to analyze and sort freshly isolated adipocytes; however, using an adipocyte-specific reporter mouse, we demonstrate that these studies fail to detect the majority of white adipocytes. We define critical settings required for adipocyte flow cytometry and provide a rigid strategy for analyzing and sorting white and brown adipocyte populations. The applicability of our protocol is shown by sorting mouse adipocytes based on size or UCP1 expression and demonstrating that a subset of human adipocytes lacks the beta(2)-adrenergic receptor, particularly in the insulin-resistant state. In conclusion, the present study confers key technological insights for analyzing and sorting mature adipocytes, opening up numerous downstream research applications.
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| 7. |
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| 8. |
- Holmström, Therese E., et al.
(author)
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Non-transactivational, dual pathways for LPA-induced Erk1/2 activation in primary cultures of brown pre-adipocytes
- 2010
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In: Experimental Cell Research. - : Elsevier BV. - 0014-4827 .- 1090-2422. ; 316:16, s. 2664-75
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Journal article (peer-reviewed)abstract
- In many cell types, G-protein-coupled receptor (GPCR)-induced Erk1/2 MAP kinase activation is mediated via receptor tyrosine kinase (RTK) transactivation, in particular via the epidermal growth factor (EGF) receptor. Lysophosphatidic acid (LPA), acting via GPCRs, is a mitogen and MAP kinase activator in many systems, and LPA can regulate adipocyte proliferation. The mechanism by which LPA activates the Erk1/2 MAP kinase is generally accepted to be via EGF receptor transactivation. In primary cultures of brown pre-adipocytes, EGF can induce Erk1/2 activation, which is obligatory and determinant for EGF-induced proliferation of these cells. Therefore, we have here examined whether LPA, via EGF transactivation, can activate Erk1/2 in brown pre-adipocytes. We found that LPA could induce Erk1/2 activation. However, the LPA-induced Erk1/2 activation was independent of transactivation of EGF receptors (or PDGF receptors) in these cells (whereas in transformed HIB-1B brown adipocytes, the LPA-induced Erk1/2 activation indeed proceeded via EGF receptor transactivation). In the brown pre-adipocytes, LPA instead induced Erk1/2 activation via two distinct non-transactivational pathways, one G(i)-protein dependent, involving PKC and Src activation, the other, a PTX-insensitive pathway, involving PI3K (but not Akt) activation. Earlier studies showing LPA-induced Erk1/2 activation being fully dependent on RTK transactivation have all been performed in cell lines and transfected cells. The present study implies that in non-transformed systems, RTK transactivation may not be involved in the mediation of GPCR-induced Erk1/2 MAP kinase activation
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| 9. |
- Isidor, Marie S., et al.
(author)
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An siRNA-based method for efficient silencing of gene expression in mature brown adipocytes
- 2016
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In: Adipocyte. - : Informa UK Limited. - 2162-3945 .- 2162-397X. ; 5:2, s. 175-185
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Journal article (peer-reviewed)abstract
- Brown adipose tissue is a promising therapeutic target for opposing obesity, glucose intolerance and insulin resistance. The ability to modulate gene expression in mature brown adipocytes is important to understand brown adipocyte function and delineate novel regulatory mechanisms of non-shivering thermogenesis. The aim of this study was to optimize a lipofection-based small interfering RNA (siRNA) transfection protocol for efficient silencing of gene expression in mature brown adipocytes. We determined that a critical parameter was to deliver the siRNA to mature adipocytes by reverse transfection, i.e. transfection of non-adherent cells. Using this protocol, we effectively knocked down both high-and low-abundance transcripts in a model of mature brown adipocytes (WT-1) as well as in primary mature mouse brown adipocytes. A functional consequence of the knockdown was confirmed by an attenuated increase in uncoupled respiration (thermogenesis) in response to beta-adrenergic stimulation of mature WT-1 brown adipocytes transfected with uncoupling protein 1 siRNA. Efficient gene silencing was also obtained in various mouse and human white adipocyte models (3T3-L1, primary mouse white adipocytes, hMADS) with the ability to undergo browning. In summary, we report an easy and versatile reverse siRNA transfection protocol to achieve specific silencing of gene expression in various models of mature brown and browning-competent white adipocytes, including primary cells.
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| 10. |
- Isidor, Marie S., et al.
(author)
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Pyruvate kinase M2 represses thermogenic gene expression in brown adipocytes
- 2020
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In: FEBS Letters. - : Wiley. - 0014-5793 .- 1873-3468. ; 594:7, s. 1218-1225
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Journal article (peer-reviewed)abstract
- Utilizing the thermogenic capacity of brown adipose tissue is a potential anti-obesity strategy; therefore, the mechanisms controlling expression of thermogenesis-related genes are of interest. Pyruvate kinase (PK) catalyzes the last step of glycolysis and exists as four isoenzymes: PK, liver, PK, red blood cell, PK, muscle (PKM1 and PKM2). PKM2 has both glycolytic and nuclear functions. Here, we report that PKM2 is enriched in brown adipose compared with white adipose tissue. Specific knockdown of PKM2 in mature brown adipocytes demonstrates that silencing of PKM2 does not lead to a decrease in PK activity, but causes a robust upregulation of thermogenic uncoupling protein 1 (Ucp1) and fibroblast growth factor 21 (Fgf21) gene expression. This increase is not mediated by any of the known mechanisms for PKM2-regulated gene expression, thus implying the existence of a novel mechanism for PKM2-dependent effects on gene expression.
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